Protocol for Testing Fouled Railway Ballast in Large-Scale Cyclic Triaxial Equipment

A testing protocol was developed to measure accumulation of vertical plastic deformation in fouled railway ballast under cyclic traffic loading. Large-scale cyclic triaxial (LSCT) test equipment was constructed to test fouled ballast under various stress conditions. A method of introducing fouling material and moisture to ballast specimens was critical to the resulting deformational behavior. Specimens for LSCT testing should be prepared by mixing ballast with relatively dry fouling material (moisture <5 % for granular fouling and <15 % for clay-based fouling) prior to compaction to prevent a heterogeneous distribution of fouling within the specimen. A full-scale track model experiment (FSTME) was built to determine a representative state of stress (RSS) for railway ballast for use in the LSCT testing. The RSS allows for testing of ballast under consistent stresses to compare the effect of material characteristics of fouling such as fouling content and moisture content. A RSS of 90 kPa (confining) and 300 kPa (deviator) for a train axle load of 264 kN was suggested based on the FSTME results. Measured deformation of fouled ballast using the proposed testing protocol was compared with a published vertical deformation of railway track in a track test section. Results of this study indicate that the proposed testing protocol can simulate the vertical plastic deformation of railway ballast at a specified stress level.